A substrate processing system used in this type of application in the related art may adopt a cluster tool (multi-chamber) structure with a plurality of process modules connected around a main transfer chamber (common transfer chamber) so as to integrate the flow of various processes to smooth the flow of the processes or to enable execution of more diverse processes. Typically, such a substrate processing system is adopted in conjunction with a semiconductor manufacturing apparatus (see, for instance, Japanese Laid Open Patent Publication No. 2000-127069).
A cluster tool utilized for, for instance, thin-film formation includes a load-lock module connected to the main transfer chamber via a gate valve. When executing a specific type of processing on substrates to be processed (hereafter to be referred to simply as “substrates”) such as semiconductor wafers (hereafter also referred to simply as “wafers”), the main transfer chamber as well as the individual process module chambers is sustained in a state of vacuum. After a wafer is transferred into a load-lock module that is at one atmosphere (atmosphere-side pressure), the load-lock module is depressurized to a low pressure state (vacuum-side pressure). The wafer is then taken out of the load-lock module on the vacuum side and is carried into the main transfer chamber by a transfer mechanism (such as a robot arm) installed in the main transfer chamber from which it is transferred into the first process module by the transfer mechanism.
In the first process module, a first processing step is executed for a predetermined length of time based upon a preset recipe. During the first processing step, film formation, for instance, may be executed to form a first thin-film layer on the wafer. Once the first processing step ends, the wafer having undergone the first processing step is carried out from the first process module by the transfer mechanism installed in the main transfer chamber and is carried into the second process module.
In the second process module, a second processing step is executed over a predetermined length of time based upon a preset recipe as in the first process module. During the second processing step, film formation, for instance, may be executed to form a second thin-film layer over the first layer having been formed on the wafer. Once the second processing step ends, the wafer having undergone the second processing step is carried out of the second process module by the transfer mechanism in the main transfer chamber and if it is to further undergo a subsequent processing step, it is carried into the next process module (e.g., a third process module) and undergoes the next processing step for a predetermined length of time. The semiconductor wafer thus undergoes various processing steps and when all the processing steps have been executed, the semiconductor wafer is carried back into the load-lock module.
As the processed wafer having undergone the series of processing steps in the individual process modules is transferred back into the load-lock module and the pressure inside load-lock module is switched from the vacuum-side pressure to the atmosphere-side pressure. The processed wafer is then carried out of the load-lock module via a wafer intake/outlet located on the side opposite from the side where the main transfer chamber is connected.
This type of cluster tool is ideal in applications in an in-line substrate processing system that executes a series of processing (e.g., film formation processing and heat treatment) on a batch of wafers sequentially transferred to a plurality of process modules at vacuum-side pressure, one wafer at a time.
In a cluster tool such as that described above, the transfer mechanism in the main transfer chamber is normally able to access a single process module at a time, i.e., the transfer mechanism is not normally able to access two process modules at once. Accordingly, the transfer mechanism accesses one of the process modules at a time to transfer a wafer into the process module. Then, the processing is executed in the individual process modules over the predetermined lengths of time according to the corresponding recipes (process jobs), and the processed wafer is carried out of a process module where the recipe processing has been completed if the transfer mechanism is not currently engaged in a transfer of another wafer.
When the batch of wafers is processed in the various process modules over varying lengths of processing time in, for instance, a pipeline system, the recipe processes executed in the plurality of process modules may end with conflicting timing or at time points too close to one another due to different processing cycles in the individual process modules. For this reason, the timing with which a wafer should be carried into/out of a given process module may conflict with the wafer transfer timing for another process module.
More specifically, in the cluster tool described above, for instance, the recipe process executed in the first processing step in the first process module may end while a wafer having undergone the second recipe process executed in the second processing step in the second process module and taken out of the second process module is being transferred toward the load-lock module by the transfer mechanism. Under such circumstances, the transfer mechanism first transfers the wafer having undergone the second processing step to the load-lock module, then accesses the first process module, takes out the wafer having undergone the first processing step and transfers it into the second process module.
Such a wafer a transfer procedure is less than ideal in that the transfer efficiency and the process module operation rates are not maximized. In more specific terms, after the processing period in the first step ends in the first process module, the wafer having undergone the first processing step must be kept in standby in the first process module until the transfer mechanism becomes available to carry the wafer out of the first process module in the example described above.
In this situation, if the total length of required time per wafer corresponding to the first process module, which includes the length of the first processing step, the length of time required to transfer the wafer into the first process module and the length of time required to transfer the wafer out of the first process module, is the largest among all the process modules (if the total length of required time per wafer is greater than any of the total lengths of time per wafer corresponding to all the other process modules), the greatest total length of time required per wafer is even further lengthened by the length of time during which the wafer having undergone the first processing step is kept in standby. The lengthened processing cycle resulting from the extended total length of required time per wafer in the first process module, which is the greatest among the plurality of process modules in the first place, is bound to affect the transfer tactic in the entire cluster tool.
At the same time, the next wafer to be processed is not carried into the second process module immediately after the wafer having undergone the second processing step is carried out and thus, the gate valve is closed. Only after transferring the wafer having undergone the second processing step to the load-lock module, the transfer mechanism accesses the first process module to transfer the wafer having undergone the first processing step from the first process module to the second process module for the second processing step. Thus, after the wafer having undergone the second processing step is carried out of the second process module, a time lag ensues before the gate valve is opened again to allow the next wafer to be carried in.
Since the processed wafer and the next wafer to undergo the processing cannot be carried out and carried in at once, as described above, the open/close operation of the gate valve, the transfer operation by the transfer mechanism and the like must be executed many times, which is bound to lower the throughput. In addition, a wait period occurs in the second process module before the recipe process on the next wafer can be started. Thus, if the total length of time required per wafer corresponding to the second process module is the greatest among all the process modules, the time length of the cycle (or interval) corresponding to the greatest total length of time required per wafer at the second process module is further increased by the extent corresponding to the length of the wait period. In such a case, too, the transfer tactic in the entire system is adversely affected. Such deterioration in the transfer tactic is bound to result in reduced operation rates of the process modules and lowered throughput.
Furthermore, post-processing (after recipe process) such as an N2 purge may be executed after the wafer having undergone the recipe process is carried out of a given process module. The next wafer to undergo the processing cannot be carried into the process module while this post-processing is in progress. If such post-processing is executed in the process module requiring the greatest total length of time per wafer, the total length of required time is further extended, which causes further deterioration of the transfer tactic in the overall system.